140 Chapter 2: Ethernet LANs
Ethernet LAN Segments
Segment length (the maximum length) is an important consideration when using Ethernet
technology in a LAN. This topic describes segments and their limitations.
A segment is a network connection made by a single unbroken network cable. Ethernet
cables and segments can span only a limited physical distance, beyond which transmissions
will become degraded because of line noise, reduced signal strength, and failure to follow
the carrier sense multiple access collision detect (CSMA/CD) speci?¬?cations for collision
detection.
Here are guidelines for understanding Ethernet cable speci?¬?cations, using 10BASE-T as an
example:
?– 10 refers to the speed supported, in this case 10 Mbps.
?– BASE means it is baseband Ethernet.
?– T means twisted-pair cable, Category 5 or above.
Each connection speci?¬?cation distinguishes some characteristics. For example, 10BASEFL
would be 10 Mbps, baseband, over ?¬?ber-optic (FL indicates ?¬?ber link). Each type of
Ethernet network also has a maximum segment length. Table 2-1 describes the different
Ethernet speci?¬?cations.
Table 2-1 Ethernet Segment Distance Limitations
Ethernet
Specification Description Segment Length
10BASE-T 10-Mbps Ethernet over twisted-pair 100 m
10BASE-FL 10-Mbps over ?¬?ber-optic cable 2000 m
100BASE-TX 100-Mbps Ethernet over twistedpair
100 m
100BASE-FX Fast Ethernet, still 100-Mbps, over
?¬?ber-optic cable
400 m
1000BASE-T Gigabit Ethernet, 1000-Mbps, over
twisted-pair
100 m
1000BASE-LX Gigabit Ethernet over ?¬?ber-optic
cable
550 m if 62.
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